Feasibility of using Chlorella vulgaris for the removal of selenium and chromium in water: Competitive interactions with sulfur, physiological effects on algal cells and its resilience after treatment

The present study was to assess the feasibility of the use of Chlorella vulgaris to remove selenium (Se) and chromium (Cr) by investigating the removal efficiency, interactions with sulfur (S), toxicity to the alga and its resilience. When exposed to only Se, S or Cr, C. vulgaris showed the greatest removal efficiency for Se (95.24%), followed by S (80.01%) and Cr (59.91%). When simultaneously exposed to all the elements, the opposite results were obtained with the affinity order as follows: Cr > S > Se. After exposure, 62.20% of the accumulated Se was continuously volatilized into the atmosphere, while 34.16% of the Cr was released back to the water. The decline in the growth of chlorophyll content and photosynthesis activity indicates the inhibitory effects of Se and Cr on the alga, which apparently wore off over time. The resilience of the Se/Cr-treated alga was confirmed by the recovery of antioxidant activities, particularly SOD, and MDA content within 72h. Our findings suggest the bioremediation of Se/Cr using C. vulgaris would be promising and sustainable due to its great performance and resilience, while the selectivity order provides insights into the competition among S, Se and Cr, revealing the actual removal capacity in the field.